Magnetic core box



July 26, 1960 c. w. LUFCY MAGNETIC CORE BOX.

Filed March 17, 1 959 INVENTOR Carroll WLzLfg/ ATTORNEYS United StatesPatent MAGNETIC CORE B'ox Carroll W. Lufcy, Silver Spring, Md., assignorto Dynacor Inc., Kensington, Md., a corporation of Maryland Filed Mar.17, 1959, Ser. No. 800,019

8 Claims. (Cl. 336-213) This invention relates to a box or container fora magnetic core, and more particularly to a container for a tape-woundmagnetic core.

This application is a continuation-in-part of prior application SerialNo. 595,980, filed July 5, 1956 and now abandoned.

Currently, tape-wound magnetic cores are widely used in variouselectrical and electronic applications, such as -magnetic amplifiers,magnetic memories for computors,

etc. In these applications, it is highly important that the corecontainer or box satisfies a number of stringent requirements.

Primarily, the container must be rigid to preserve and protect themagnetic characteristics of the tape-wound core which is highly strainsensitive. Since these containers are frequently immersed or potted invarious oils and compounds, they must be sealed against inward seepageof these compounds. Furthermore, a cross-sectional configuration whichuniformly spaces a wound coil about the magnetic core within the boxwith a minimum distance between a coil and the core is desirable. Inaddition, to facilitate application and preservation of the wind ings aswell as providing a neat and attractive appearance, the external surfaceof the container should be substantially smooth. Still further, thecontainer must not provide a complete conductive circuit about thewinding. A practical container must fulfill these stringent requirementswith a structure which is simple and economical to manufacture. None ofthe boxes or containers heretofore proposed have provided a structurewhich satisfies all of these aforementioned demands.

An object of this invention is to provide a container for a magnetictape-wound core having a simple structure well adapted for economicalfabrication which simultaneously fulfills all of the aforementionedrequirements for a commercially acceptable enclosed tape-wound magneticcore.

In accordance with this invention, an enclosed magnetic tape-wound coreincludes a toroidal wound core of magnetic tape disposed within athin-walled hollow anodizable metal toroidal container having an openside. A suitable cushioning material separates the core from adjacentsurfaces of the container and the lid which closes the open side of thecontainer. This lid is also made of anodizable metal, and both the lidand the container are anodized before assembly to insure that theiradjacent surfaces are insulated from each other to break any closedcircuits about the core which might be formed by these conductive metalelements. Both inner circumferential edges of the container areinternally recessed to provide shoulders for supporting the lid, andboth circumferential edges of the outer surface of the lid are alsorecessed to interlock within the edges of the container when they aredeformed to lock over the lid and seal the open end of the container. Athin sheet of material having a slick non-wetting surface, such asTeflon, is disposed between the container and lid before it is sealed2,946,973 Patented July 26, 1960 to form a liquid-tight joint betweenthe lid and container when merely enough pressure to form a visuallysmooth joint is applied to interlock the edges of the container with thelid. This slight pressure is suiiicient to satisfactorily seal the jointbetween the container and lid against liquid seepage without applyingenough force to adjacent portions of the container, sheet or lid tobreak through the insulation provided by the anodized coating and sheet.

Novel features and advantages of the present invention will becomeapparent to one skilled in the art from a reading of the followingdescription in conjunction with the accompanying drawings whereinsimilar reference characters refer to similar parts and in which:

Fig. l is a perspective view of an embodiment of this invention incompleted form;

Fig. 2 is a view in elevation partially broken away to illustrate across section of an embodiment of this invention; and

Fig. 3 is a portion of a cross-sectional view in elevation of a portionof another embodiment of this invention.

In Fig. l, a finished and assembled enclosed magnetic core 10 is shownto illustrate the neat and attractive, as 'well as functional, structureof a core 10 made in accordance with this invention. This core 10includes a metal container 12 and a lid 14. Various features of thisinvention, later described in detail, cooperate to provide its highlyfunctional and attractive structure. All surfaces of this core joinsmoothly and continuously to facilitate the application and preservationof windings or coils. All corners are, accordingly, rounded whichgreatly facilitates coil winding and prevents snagging or tearing of thecoils after they are wound. The container 12 is made, for example, ofaluminum to provide necessary rigidity without introducing unnecessarybulk. Aluminum is light, machineable and ductile, yet fairly strong. Thelid 14 is also made, for example, of aluminum, and these containers maybe provided in a variety of sizes, ranging from small to large,including boxes having fractional inch diameters and those severalinches in diameter. ranging up to six inches in outside diameter and upto one inch high, the wall and lid thicknesses of representativealuminum boxes range, for example, from 0.020 inch to 0.050 inch.

As shown in Fig. 2, core 10a includes an open-sided hollow toroidal ordoughnut-shaped container 12:: fabricated of aluminum, for example. Atape winding 16a of typical construction is placed within the cavity 18aprovided within the metal container 12a. Tape winding 16a is surroundedby a body of cushioning material 20a which may be, for example, anunvulcanized rubber not including a vulcanizing agent. A siliconematerial, such as nvulcanized Silastic, may be used to advantage. Thewinding and cushioning substance are maintained below the shoulders 22aprovided by the internally recessed edges 23a and 24a of the container.Edge 23a is shown before it is deformed to seal the container, and edge24a is shown in the sealed condition. A gasket 26a is interposed betweenthe lid 14a and the edges and contents of the container. The clearancebetween the annular lid 14:: and the edges of the container are selectedto permit the gasket to be interlocked between the lid and containerwalls. Both circumferential edges 280 on one side of the lid 14a arenotched or recessed to provide a space for receiving the deformed edges23a and 24a of the container 12a and the gasket 26a. When the edges 23aand Z Z-a are rolled inwardly to lie within the recesses 28a in the lid14a, the gasket 26a accordingly forms a tortuous path between theinterlocked edges of the body and the lid. The outer surface of thecontainer is maintained smooth by virtue of the interlocking of theedges of the body For boxes within the recesses in the lid. I Anyprotruding portions of the gasket 26a are cut off clean with theexterior of the container surface to preserve the smooth exterior of thesurface.

Gasket 26a is made, for example, of a thinsheeti'of slicknon-Wettingrnaterial which provides a liquid-tight joint between theinterlocked edgesof the container and lid even though they are onlydeformed together by'a force which is just sufiicient to provide avisually sealed joint which is pleasing to the eye. A particularlyadvantageous material for this gasket is a thin sheet of Teflon, atetrafluoroethylene polymer made by the DuPont Company of Wilmington,Delaware, which, for example, ranges in thickness from 0.002 inch to0.006 inch. This gasket, accordingly, advantageously utilizes a sheet-ofthis material which has a nominal thickness of 0.004 inch. A sheet ofthis material provides exceptional sealing characteristics and preventsliquid seepage through the joint formed between the deformed edges ofthe container and the lid even though the pressure exerted upon it bythe deformed edges is extremely slight. Furthermore, the insulatingproperties of Teflon, in conjunction with the anodized surfaces of theadjacent parts of the lid and container prevent the completion of adeleterious electrical circuit about the core through the lid andcontainer. This remarkable characteristic of this sheet of slick .material insures the maintenance of insulation between a lid and containermade of a conductive material, such as aluminum, even though Teflonalone in a thin sheet might be too fragile, and anodizing alone wouldnot dependably insulate if greatersealing pressures than the remarkablyslight ones described herein had to be utilized. The joint provided inaccordance with this invention unexpectedly provides adequate enoughinsulation and sealing characteristics to effectively prevent shortcircuits and the entrance of liquids, such as potting compounds, intothe container. Although the exact reason for the sealing phenomenon isnot fully understood, it is believed that the slick non-wetting surfaceof Teflon prevents capillary action from drawing a liquid through thejoint into the container even though crevasses of substantial magnitudemight exist. 7

Another embodiment 10b of this invention is shown in the cross-sectionalview illustrated in Fig. 3 which also, for example, shows materialsidentical to those used in Fig. 2. In Fig. 3, however, the edges 28b ofthe lid 14b are recessed by being chamfered instead of beingnotched.Recessed edges 24b of the container 12b accordinglylie over andinterlock with chamfered edges 28b of the lid 14b to form a'smoothcontinuation of container 12]) when its edges 24b are deformed."

What is claimed is:

'1. An enclosed magnetic tape-wound core comprising a toroidal woundcore of magnetic tape, a thin-walled hollow toroidal container made ofan anodizable metal 4 having an open side, said core being insertedwithin sai container, an annular lid also made of an anodizable metal,said lid being substantially rigid in its planar direction and includingrecessed circumferential edges upon its outer surface, the inner andouter edges of said circumferential container being internally recessedto provide shoulders constructed and arranged to support said lid in aposition to have its'outer surface form a substantially smoothcontinuation of the outside wall of said container when said edges ofsaid container are deformed to lie within and'to" interlock with saidrecessed edges of said lid, said lid being disposed against saidshoulders and having its recessed edges interlocked within said deformedcircumferntial edges of said container to provide a joint of substantiallengththerehetween, a cushioning material disposed within said containerseparating said core from the adjacent surfaces of said container andlid, the dimensions of said container and lid and the thickness of'saidcushioning material disposed'betwe'en said adjacent surfaces beingconstructed and arranged to pro vide a substantially uniformperpendicular dimension from the outer surfaces of said core torespective closest outer surfaces of said container and lid, the'surfaceof said container and lid being anodized to provide insulation betweensaid lid and said container, and a thin sheet of insulating materialhaving a slick non-wetting surface being interposed between said lid andsaid container and interlocked within said joint between said deformedcircumferential edges'of said container and said recessed edegs of saidlid to provide an effective liquid-tight'seal and insulation betweensaid lid and container when only enough force is appliedto deform saidcircumferential edges sufliciently to provide a visually smooth joint.

2. An enclosed magnetic tape-wound core as set forth in claim 1 whereinsaid sheet is comprised of Teflon.

3. An enclosed magnetic tape-wound core as set forth in claim 2 whereinsaid sheet of Teflon ranges in thickness from 0.002 inch to 0.006 inch.

4. An enclosed magnetic tape-wound core as set forth in claim 3 whereinsaid sheet of Teflon is 0.004 inch thick.

5. An enclosed magnetic tape-wound core as set forth in claim 3 whereinthe wall thickness of said container and said lid ranges from 0.020 inchto 0.050 inch.

6. An enclosed magnetic tape-wound core as setforth in claim 1 whereinsaid edges of said lid are sharply notched. v e

'7. An enclosed magnetic tape-wound core .as set forth in claim lwhereinsaid edges of said lid are chamfered.

8. An enclosed magnetic core as set forth in claim l wherein saidcontainer and said lid are made of aluminum.

References Cited in the file of this patent Special Magnetic Alloys andApplications, pp.. 843- 845, Electrical Engineering, September 1948.

